Wind turbines have become a preferred source of renewable energy in the developed world, resulting in a continued effort to improve turbine output and efficiency. This has lead to development and production of physically larger wind turbine designs.
Due to the continual increase in component size, modern wind turbines can experience mechanical problems not previously an issue with smaller-dimensioned designs. One of these issues is that of blade root ovalisation.
A wind turbine blade root generally comprises a plurality of connecting elements projecting from the circular root end, e.g. blade root bushings, stay bolts, flanges, etc., for connection of the wind turbine blade to a wind turbine hub, wind turbine hub extender and/or pitch system. As stay bolts are normally used to bear the considerable forces involved in the mounting of a wind turbine blade, it is essential that such stay bolts are connected between wind turbine components with a high degree of accuracy. Any misalignment between stay bolts and/or apertures to receive such stay bolts can result in stay bolts provided in blade root bushings to touch or brush against the side of the root bushing, the root flange, and/or the pitch bearing. Such a direct contact can have a serious effect on the dynamic strength of the stay bolt, and it must be avoided to avoid untimely failure of stay bolt connections.
Furthermore, a known problem in wind turbine manufacture is blade root ovalisation after blade moulding, wherein the natural forces present in a blade root section act to force the nominally circular blade root towards an oval shape. Such a ovalisation considerably complicates the act of accurate alignment of blade root components during mounting or coupling operations.
Current construction methods can involve the use of a jacking mechanism to jack sections of the wind turbine blade root to assume a circular shape, to aid with the mounting of the blade root flange, and/or when subsequently mounting the blade on the turbine. However, such a system does not provide for an even roundness of the root end, which can result in misalignments between blade root components. Further, once the jacking force is removed, the blade root end will act to return to the natural oval shape.
An example of a prior art system for wind turbine blade mounting is provided in EP 2 453 129, which uses guiding bushings having a tapered end to guide a blade root with respect to a mounting flange.
It is an object of the invention to provide a method and system which allows for improved alignment of blade root ends with subsequent wind turbine components, as well as for minimising the effects of wind turbine blade root ovalisation, thereby improving the durability of wind turbine components.